diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6706779a91d84..6e829bd518a7e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -193,6 +193,10 @@ ELSE()
   SET (SKIP_COMPONENTS "N-O-N-E")
 ENDIF()
 
+SET(IO_SIZE "" CACHE STRING "Specify the I/O buffer size")
+IF(IO_SIZE)
+  ADD_DEFINITIONS(-DIO_SIZE=${IO_SIZE})
+ENDIF()
 
 SET(MEMPROTECT_DEFAULT ON)
 
diff --git a/include/my_global.h b/include/my_global.h
index 76ec2f813083e..5b349904fbfc5 100644
--- a/include/my_global.h
+++ b/include/my_global.h
@@ -676,7 +676,9 @@ typedef SOCKET_SIZE_TYPE size_socket;
   This influences the speed of the isam btree library. E.g.: too big too slow.
   4096 is a common block size on SSDs.
 */
+#ifndef IO_SIZE
 #define IO_SIZE			4096U
+#endif
 #if ((IO_SIZE <= 0) || ((IO_SIZE % 512) != 0) || ((IO_SIZE & (IO_SIZE-1)) != 0))
 #error "IO_SIZE must be a positive multiple of 512 and power of 2"
 #endif